1. Field of the Invention
The present invention relates to an optical switch, and in particular, to an optical switch suitably used in an optical communication apparatus, an optical transmission apparatus, and the like.
2. Description of the Related Art
As for an optical switch for switching an optical path, those for switching a traveling direction of light by electrically changing a refractive index or phase of an optical path, switching a traveling direction of light by mechanically displacing an optical path, and so on have been developed. The mechanical optical switch has been often used in an optical communication apparatus, optical transmission apparatus, or the like because it has a low coupling loss of light, is substantially independent of the wavelength of the propagating light, and have a self-latching property for maintaining, even after removal of electric power, the coupling state of light in a state before the removal.
The mechanical optical switch comprises a movable optical fiber which can be elastically deformed and two fixed optical fibers, an open end of the movable optical fiber facing to open ends of the fixed optical fibers via an optical gap, and switches the optical path by displacing the open end of the movable optical fiber with respect to the open ends of the fixed optical fibers. A silicone based liquid serving as an index matching oil is placed between the open end of the movable optical fiber and those of the fixed optical fibers in order to prevent attenuation and scattering of light from occurring there. For that purpose, the whole mechanism of the optical switch is contained in a housing, and the housing is filled with the silicone based liquid.
The fixed optical fibers are held by a fixed holder (fixed block) at portions close to their open ends. The movable optical fiber is held by a movable holder (movable block) at a portion close to its open end. The movable optical fiber is held by another fixed holder at a point distant from the tip of the movable optical fiber, and the point constitutes a fulcrum.
Since the open ends of the fixed optical fibers and the open end of the movable optical fiber are provided to face to each other, the fixed holder and the movable holder also face to each other. In order to displace the open end of the movable optical fiber with respect to the open ends of the fixed optical fibers, the movable holder is displaced with respect to the fixed holder. In order to keep such a movement within a certain route for avoiding misalignment when displacing the movable holder with respect to the fixed holder, guide pins are provided on one of the holders (for example, fixed holder) to protrude from the facing surface thereof and are inserted into guide channels provided on the facing surface of the other holder (for example, movable holder). Thus, when the movable holder is displaced, the guide pins move along the guide channels, and the movable holder is stopped when the guide pins reach the ends of the guide channels.
An electromagnetic actuator is used to displace the movable holder or movable optical fiber with respect to the end of the fixed optical fiber, which is typically large in size. The movable holder or movable optical fiber is moved in the index matching oil having viscosity, so that a significant magnitude of force is required. For that purpose, a large electromagnetic actuator is required. The housing of the optical switch is intended to contain the large electromagnetic actuator therein, so that it also becomes large in size. In addition, since the optical switch circuit includes a combination of many optical switches, if the individual optical switches are large, the optical switch circuit is also large.
U.S. Pat. No. 6,169,826 (issued on Jan. 2, 2001) has been proposed to reduce the size of an electromagnetic actuator used in an optical switch. The structure thereof will be described below with reference to FIG. 6.
Referring to FIG. 6, in an optical switch 600, fixed optical fibers 624 and movable optical fibers 622 are positioned so as to have their respective open ends faced to each other in a housing 610. The open ends of the movable optical fibers are moved relatively to the open ends of the fixed optical fibers to connect and/or disconnect an optical path. The fixed optical fibers are held by a fixed holder 632 made of soft magnetic ceramic at a portion close to the open ends thereof in the housing 610. The movable optical fibers 622 are supported and fixed in the housing 610 by another fixed holder 636 at a distance from the open ends thereof and are held by a movable holder 634 made of soft magnetic ceramic at a portion close to the open ends thereof. When the movable holder 634 made of soft magnetic ceramic is reciprocated with respect to the fixed holder 632 made of soft magnetic ceramic, the open ends of the movable optical fibers held by the movable holder 634 made of soft magnetic ceramic are reciprocated with respect to the tips of the fixed optical fibers 624 along with the movable holder 634 to connect and/or disconnect the optical path.
An electromagnetic actuator 650 comprises an E-shaped yoke 652 having a back yoke (column yoke) 654 which is located on the side of the fixed optical fibers 624 from the fixed holder 632 made of soft magnetic ceramic in the housing, and first and second end legs 656 and 656xe2x80x2 of the E-shaped yoke 652 extend from the back yoke 654 to the side surfaces of the movable holder 634 made of soft magnetic ceramic. The first and second end legs 656 and 656xe2x80x2 have first and second pole pieces 658 and 658xe2x80x2, respectively, which face the side surfaces of the movable holder 634 made of soft magnetic ceramic. The movable holder 634 made of soft magnetic ceramic can reciprocate between the first and second pole pieces 658 and 658xe2x80x2. A center leg 662 protruding from the center of the back yoke 654 toward the movable holder 634 made of soft magnetic ceramic is constituted by a permanent magnet 664 and the fixed holder 632 made of soft magnetic ceramic. For example, the permanent magnet 664 may be a sintered neodymium-iron-boron permanent magnet.
The permanent magnet 664 is magnetized in a direction from the fixed holder 632 made of soft magnetic ceramic to the back yoke 654 or in the direction opposite thereto. Part of the magnetic flux exiting from the permanent magnet 664 enters the first end leg 656 through the back yoke 654. Then, it enters the movable holder 634 made of soft magnetic ceramic via the first pole piece 658. Then, it passes through the fixed holder 632 made of soft magnetic ceramic to return to the permanent magnet 664. In this way, the permanent magnet 664, a first half of the back yoke 654, the first end leg 656, the first pole piece 658, the movable holder 634, and the fixed holder 632 constitute a first magnetic path. The magnetic flux of the permanent magnet passing through the first magnetic path is denoted by reference symbol A in this drawing.
Part of the magnetic flux exiting from the permanent magnet 664 enters the second end leg 656xe2x80x2 through the back yoke 654. Then, it enters the movable holder 634 made of soft magnetic ceramic via the second pole piece 658xe2x80x2. Then, it passes through the fixed holder 632 made of soft magnetic ceramic to return to the permanent magnet 664. In this way, the permanent magnet 664, a second half of the back yoke 654, the second end leg 656xe2x80x2, the second pole piece 658xe2x80x2, the movable holder 634, and the fixed holder 632 constitute a second magnetic path. The magnetic flux of the permanent magnet passing through the second magnetic path is denoted by reference symbol B in this drawing.
FIG. 6 shows a state in which the movable holder 634 made of soft magnetic ceramic is attracted by the first pole piece 658, and there is a wider gap between the movable holder and the second pole piece 658xe2x80x2. The optical switch 600 comprises four fixed optical fibers 624 (denoted by reference symbols f1, f2, f3, and f4 from the left) and two movable optical fibers 622 (denoted by reference symbols m1 and n2 from the left). When the movable holder 634 made of soft magnetic ceramic is attracted by the first pole piece 658, the fixed optical fiber f1 and the movable optical fiber m1 have their open ends face each other, and the fixed optical fiber f3 and the movable optical fiber m2 have their open ends face each other, thereby establishing optical paths between them respectively. On the other hand, when the movable holder 634 made of soft magnetic ceramic is attracted by the second pole piece 658xe2x80x2, optical paths are established between the fixed optical fiber f2 and the movable optical fiber m1, and between the fixed optical fiber f4 and the movable optical fiber m2. Displacing the movable holder 634 from the first pole pieces 658 to the second pole piece 658xe2x80x2 can switch the position of the movable optical fiber m1 from the fixed optical fiber f1 to f2, and the position of the movable optical fiber m2 from the fixed optical fiber f3 to f4.
First and second coil members 672 and 672xe2x80x2 are wound around the first and second end legs 656 and 656xe2x80x2, respectively. When a current for canceling or decreasing the magnetic flux A is applied to the first coil member 672, and a current having a direction intended to increase the magnetic flux B is applied to the second coil member 672xe2x80x2, the attraction between the movable holder 634 and the first pole piece 658 is vanished, and then the movable holder 634 is attracted to the second pole piece 658xe2x80x2 to move toward the second pole piece 658xe2x80x2. When the movable holder 634 is attracted by the second pole piece 658xe2x80x2, the optical paths are established in such a manner that the movable optical fiber m1 is connected to the fixed optical fiber f2 and the movable optical fiber m2 is connected to the fixed optical fiber f4. If the current applied to the first and second coil members 672 and 672xe2x80x2 is stopped in this state, the state in which the movable holder 634 is attracted by the second pole piece 658xe2x80x2 is maintained by the permanent magnet 664.
If a current for canceling or decreasing the magnetic flux B is applied to the second coil member 672xe2x80x2, and a current for increasing the magnetic flux A is applied to the first coil member 672 when the movable holder 634 is attracted by the second pole piece 658xe2x80x2, the movable holder 634 leaves the second pole piece 658xe2x80x2 and moves toward the first pole piece 658. Then, as shown in FIG. 6, the movable optical fiber m1 is connected to the fixed optical fiber f1, and the movable optical fiber m2 is connected to the fixed optical fiber f3. If the current applied to the coil members 672 and 672xe2x80x2 is stopped in this state, the connections are maintained.
In case of the electromagnetic actuator according to the above-described U.S. Patent, downsizing is realized by utilizing the movable holder 634 and fixed holder 632 both made of soft magnetic ceramic as part of the magnetic circuit of the electromagnetic actuator 650.
Since the fixed holder 632 is utilized as part of the magnetic circuit, however, most parts of the electromagnetic actuator 650 are provided on the side of the fixed optical fiber 624 in the optical switch 600. The length of the movable optical fiber 622 from its fulcrum to its open end is required to be enough for allowing a portion thereof from the fulcrum to the open end, in particular, to the point supported by the movable holder, to elastically pivot without undergoing an excessive force. For this reason, this portion of the movable optical fiber cannot be shortened.
Therefore, the optical fiber has a length more than the sum of the length from the fulcrum to the open end of the movable optical fiber and the length of the electromagnetic actuator. The electromagnetic actuator includes the coil members. If the length of the electromagnetic actuator is reduced, the length of the coil member should also be reduced. Therefore, in order to ensure the same level of ampere-turn, the coil is rolled up to increase the number of overlap accordingly. As a result, the coil has an increased diameter, and it becomes required to increase the size of the housing of the optical switch for containing the electromagnetic actuator.
Therefore, an object of the invention is to provide an optical switch further reduced in size compared with the optical switch proposed in the U.S. Pat. No. 6,169,826.
An optical switch for connecting and/or disconnecting an optical path according to the present invention comprises:
a housing;
at least one fixed optical fiber having an open end in the housing; at least one movable optical fiber having an open end capable of moving relatively to the open end of the fixed optical fiber, the open end of the movable optical fiber being located in the housing;
a fulcrum fixing the movable optical fiber at a distance from the open end of the movable optical fiber; and
a movable holder of magnetic material fixing the movable optical fiber near the open end of the movable optical fiber and allowing the movable optical fiber to elastically pivot on the fulcrum to move the open end of the movable optical fiber relatively to the open end of the fixed optical fiber,
in which an electromagnetic actuator reciprocating the movable holder is located in an area on the movable optical fiber side from the open end of the movable optical fiber in the housing.
The electromagnetic actuator preferably comprises:
a first yoke having a first pole piece;
a second yoke having a second pole piece,
the movable holder being placed between the first and second pole pieces so as to reciprocate between the two pole pieces;
a permanent magnet exerting a magnetic flux on the first and second yokes and the movable holder, the permanent magnet constituting a first magnetic path along with the first yoke and the movable holder and constituting a second magnetic path along with the second yoke and the movable holder;
a first coil member wound around the first yoke to adjust the magnetic flux between the movable holder and the first pole piece; and
a second coil member wound around the second yoke to adjust the magnetic flux between the movable holder and the second pole piece.
The electromagnetic actuator preferably comprises an E-shaped yoke having two end legs and a center leg, the end legs constituting the first and second yokes, respectively, and the center leg having the permanent magnet. The E-shaped yoke may have a back yoke connecting the center leg to both the end legs. The back yoke may include the fulcrum on which the movable optical fiber elastically pivots.
Alternatively, in the above-described optical switch, the electromagnetic actuator may further comprise a back yoke magnetically connecting the permanent magnet to both the first and second yokes. The back yoke may include the fulcrum on which the movable optical fiber elastically pivots.
The first and second coil member may extend from the vicinities of the first and second pole pieces, respectively, to the vicinity of the back yoke.
Furthermore, the permanent magnet may be located at the end of the center leg of the E-shaped yoke to face the movable holder.
An optical switch according to the present invention comprises:
a housing having at least two end walls facing each other;
at least one fixed optical fiber having an open end near one of the end walls in the housing;
at least one movable optical fiber having an open end capable of moving relatively to the open end of the fixed optical fiber, the open end of the movable optical fiber being located in the housing;
a fulcrum fixing the movable optical fiber at a distance from the open end of the movable optical fiber and located near the other end wall in the housing;
a movable holder of magnetic material fixing the movable optical fiber near the open end of the movable optical fiber and allowing the movable optical fiber to elastically pivot on the fulcrum to move the open end of the movable optical fiber relatively to the open end of the fixed optical fiber; and
an electromagnetic actuator reciprocating the movable holder, the electromagnetic actuator being located in an area on the movable optical fiber side from the open end of the movable optical fiber in the housing.